1. Field of the Invention
The present invention relates to an air bag device in which an inflator is housed in a retainer to which a periphery of an opening of a folded air bag is fixed, and the air bag is inflated to develop by a gas which is generated by the inflator when a vehicle collides or the like (in other words, a vehicle is subject to a predetermined rapid acceleration/deceleration or more), thereby restraining an occupant.
2. Description of the Prior Art
In an air bag device of the prior art, a vent hole is formed in an air bag which is to be inflated by a gas generated by an inflator, so that the gas is partly discharged through the vent hole to control the internal pressure of the air bag. A structure of such an air bag device is proposed in which a vent hole is closed by a membrane so that an air bag is rapidly inflated in an initial development stage, and, when the development is completed and the internal pressure of the air bag is raised, the membrane is broken to discharge a gas through the vent hole, thereby gently restraining an occupant. Such as conventional air bag device can be seen in a Japanese tility Model Unexamined Publication (Kokoku) No. HEI. 5-6206.
In addition, a Japanese Patent Unexamined publication No. EI. 9-301115 suggests another air bag device in which two inflators are disposed, both the two inflators are ignited when no passenger exists in the vicinity of the air bag device, and only one of the inflators is ignited when a passenger exists in the vicinity of the air bag device, whereby the development speed and internal pressure of an air bag are controlled in accordance with the position of a passenger (see Japanese Patent Publication (Kokai) HEI 9-301115).
The conventional air bag device disclosed in the Japanese Utility Model Unexamined Publication No. HEI. 5-6206 has problems. One of the problems is that the pressure at which the membrane is broken is easily dispersed, and hence it is difficult to correctly open the vent hole when the internal pressure reaches the predetermined value. The other problem is that it is difficult to accurately control the internal pressure, because the vent hole which has been once opened cannot be again closed.
Further, the conventional air bag device disclosed in the Japanese Patent Publication (Kokai) HEI. 9-301115 also has problems. One of the problem is that the two inflators are required and hence the number of parts is increased, thereby increasing the production cost. The other problem is that the control cannot be finely conducted, because the development of the air bag is controlled in only two stages (that is, one stage in which a single inflator is ignited, or the other stage in which both inflators are ignited).